1. Field of the Invention
The present invention relates, in general, to watthour meters and, specifically, to watthour meter socket adapters for receiving plug-in watthour meters and, more specifically, to security devices for watthour meters.
2. Description of the Art
Electrical watthour meters have long been used to measure the amount of electrical power consumed by a particular machine or electrical utility customer. Watthour meters have been constructed in various configurations depending upon the type of electrical service that is required. Typically, watthour meters have a circular cross section meter mounting portion which is mounted on a wall or support surface of a building or residence. A watthour meter includes gages which indicate the amount of power consumed by the customers.
Older watthour meters of the so-called bottom connected type are formed of a single-piece housing in which the watthour meter is fixedly mounted along with terminals which provide connection between the building wiring and the external power distribution line conductors. Any defect in the watthour meter requires replacement of the entire housing. To overcome this problem, socket-type watthour meters have been devised in which the watthour meter plugs into an adapter or base having contacts connected to terminals to which the building wiring and the power line conductors are connected. This enables defective watthour meters to be easily replaced without requiring the removal of the entire housing and internal conductors.
Such socket adapters have a watthour meter receiving portion in the form of an annular side wall which extends outward from a planar base. The side wall terminates at the outer edge in a rim which mates with a corresponding mounting flange formed on the socket-type watthour meter. A sealing ring is placed about the mating rim and flange and locked in place by a suitable lock device and/or a locking tab which provides an indication of tampering.
Presently bottom connected to socket watthour meter adapters do not have a lower portion of the sealing rim. This discontinuity in the rim is provided to allow the manufacture of the housing as a single molded plastic part. Typically, this discontinuity is centered at the bottom of the rim and varies from 60.degree. to 120.degree.. Conventional sealing rings are required by industry standards to have a small gap for drainage where the ends of the sealing ring join together at the bottom of the adapter. If one skilled in the art of tampering is aware of the discontinuity in the ring, then by rotating the sealing ring so the gap in the sealing ring is at the discontinuity, by offsetting and further rotating the sealing ring, they can virtually unscrew the sealing ring and remove the watthour meter and the sealing ring as one unit without signs of tampering with the locking device.
A terminal block typically housing a plurality of screw-type terminals is mounted on the base of the bottom connected meter or socket adapter below the watthour meter receiving portion. A removable terminal cover is lockingly attached to the terminal block housing surrounding the terminal block by a suitable lock to prevent unauthorized access to the terminals. The terminal cover for bottom connected meters disclosed in U.S. Pat. No. 4,823,572 has a sealing bar which passes horizontally through a part of the cover from one side of the cover. The sealing bar has apertures which enable a seal tab to be installed to indicate tampering with the meter by inspecting the integrity of the seal. A lip is formed on one end of the sealing bar and is positioned to interfere with the rotation of the cover of the watthour meter when the cover is attached to a bottom-connected watthour meter. This prevents rotation of the meter cover and its possible unauthorized removal from the watthour meter while the terminal cover is in place.
FIG. 1 depicts a similar prior art terminal cover 10 for a watthour meter which includes a protrusion 12 integrally molded with the cover 10 and which extends inward from the cover 10 toward the base of the bottom connected watthour meter housing. The protrusion 12 engages a notch formed in the annular flange of the meter cover to prevent rotation of the meter cover. A receptacle 14 for a barrel-type lock is mounted on the terminal cover 10 for securely locking the terminal cover 10 in place to the bottom connected watthour meter housing. The protrusion provides a lock for the meter cover to concurrently lock the meter cover and the terminal cover in place.
While such security devices for lockingly mounting a terminal cover on a bottom connected watthour meter housing which include means for engaging the rotatable watthour meter cover to prevent rotation of the watthour meter cover are effective, such security devices for bottom connected to socket watthour meter adapters employ separate locks, one for the sealing ring and one for the terminal cover, for separate locking of the sealing ring and the terminal cover to the socket adapter. This adds additional cost to the socket adapter and typically may require different lock keys which complicates maintenance and authorized access to such meters by a utility company which may use several thousands of such meters.
Another prior art watthour meter socket adapter 190 is shown in FIG. 2. In this adapter 190, a discontinuity 192 was formed in the lower portion of the annular side wall and rim 194 of the adapter housing 196. A terminal cover 198 having an annular extension and rim 200 at one end was slidingly mounted in the terminal block 202 via a dovetail connection and was movable from a lowered position covering terminals 204 in the terminal block 202 to a raised position, shown in FIG. 2, to expose the terminals 204. When in the lowered position, the annular extension and rim 200 aligned with the side wall and rim 194 of the adapter housing 196 and filled the discontinuity 192 with only a small gap being formed between the sides of the annular extension and rim 200 and the adjacent edges of the side wall and rim 194 of the adapter housing 196. The sealing ring used to lock the watthour meter in the adapter 190 also engaged the annular extension and rim 200 of the terminal cover 198 to lock the terminal cover 198 in the lowered position overt he terminals 204. However, an installer was required to hold the terminal block 198 in the raised position to access the terminals 204. This made wiring connections to the terminals 204 difficult since one hand was needed to hold the terminal cover 198 in the raised position.
Thus, it would be desirable to provide a watthour meter adapter having an approved security device which can be constructed at a low cost and which securely locks the sealing ring and the terminal cover of the watthour meter adapter in place to prevent unauthorized access to the watthour meter and the terminal block. It would also be desirable to provide a security device for a watthour meter adapter which employs only one lock to securely and concurrently lock and retain the sealing ring and the removable terminal cover on the watthour meter adapter. It would further be desirable to eliminate the discontinuity in the meter sealing ring or provide a method to prevent the rotation of a sealing ring and concurrent removal of the sealing ring and watthour meter without signs of tampering.